Every tectonic fault in England is marked with a strip of tarmac, mostly wide enough for cars to pass down on either side, and with the exact location of the fault marked either with dotted white lines, or (for the more severe faults) by a central reservation and often a safety barrier between two separate tarmac bands. Major faults use an 'M' designation followed by a number. The lower the number, the more serious the fault, hence the M4 is a more serious fault than the M11. Average faults use an 'A' designation - e.g. A40, A316, and minor faults use a 'B' designation, e.g. B2216.